The present invention relates to an electromechanical protection device for a semiconductor switch to which a commutation switch is assigned.
"Hybrid switches" are combinations of semiconductor switches and mechanical switches. The mechanical switch carries a continuous current when in a "switched-on" state, while the semiconductor switch permits the current branch to be turned on and off without any arc. Since semiconductor switches are not resistant to short circuits, they require special protection devices against overly high current loads.
A known embodiment of a switching device for a sink contains a series circuit of a mechanical switch with a semiconductor switch. This arrangement switches the sink on and off in rated operation, without any arc. The semiconductor switch is switched in parallel with a commutation contact, which is provided with a drive. In the event of a short circuit, the mechanical switch is triggered by its n-trigger (or tripping device). The switching arc commutates from the contact point on a runner and is finally separated and shut off in an extinction chamber, by means of extinction plates. By commutation of the arc from the contact point to the runner, the semiconductor current branch is switched idle to the fixed contact of the mechanical switch, and the I.sup.2 t heat load of the semiconductor reaches only about 1/10 to 1/20 of the forward I.sup.2 t value. However, the semiconductor switch can be exposed to current changes with a steep increase by arc flashback between the runner and the fixed contact (U.S. Pat. No. 4,725,911).
An objective of the present invention is to improve such a known electromechanical protection device for the semiconductor switch. In particular, the commutation switch is supposed to conduct the current during rated operation and quickly relieve the semiconductor switch in case of short circuit, at the same time.